1. Field of the Invention
The instant invention relates to a method of manufacturing an overhead or underground telephone lead-in cable for voice, video, data and lead-in type services (VVDL) permitting the connection of the users to the public telephone system with high speed digital services link besides offering analog services. This is made possible through the integration of a balanced circuit to the original design of two elements made of metal, plastic or kevlar fibers, in parallel, also serving as self-supporting elements in overhead installation. Said cable is characterized because its core is protected by a moisture resistant film and is thus highly convenient for overhead or underground installation.
2. Previous Art
Generally, the overhead lead-in lines of the unitary telephone services have been limited with regard to their bandwidth and resistance to radio interferences because of their design. The demand for transmission means able to support a bandwidth large enough to meet the growing demand for digital services in the coming years also requires designs that do not increase the costs or limit the ease of installation of the current products. With regard to the cables used for the connection of the users to the telephone network, the design and method of manufacture are decisive factors. The cable should be light and economical and permit high-speed data transmission above 155 Mbps. It should also have an adequate response in frequencies above 100 Mhz and be self-supporting over distances spanning more than 100 meters. Moreover, the cable should be weather-resistant and in windy and icy conditions, it should permit its reinforcement without being necessary to modify its shape, so that the same anchorage elements usually used in this type of services can be utilized.
Among the known techniques used to solve the above-mentioned problems, in U.S. Pat. No. 4,467,138, a “conductive cable for plural communications” is described, the design of which is related to a flat communication conductor. Said flat communication conductor has two or more communication ports, polyolefin insulated cables united throughout its length arranged in groups on opposed and parallel sides of a conductive steel wire.
Even though cables presenting stranded pairs of conductors are known, not all of them have the same application, i.e., depending upon their use, the design varies in each case and even the number of pitches of the stranded pair presents differences. For example, in U.S. Pat. No. 6,064,008, a communication cable having two pair of stranded conductors is described, the main characteristic of which it is not the stranded pairs but the insulating filling material based on a chemical product of fluorinated polymer with a blowing agent. In U.S. Pat. No. 6,509,526 D, anteriority of the instant invention, a telephone lead-in cable is described for ordinary voice service and high performance Data and Video transmission services. Said cable is based on a thermoplastic sleeve, with a data transmission circuit having two metal wires helically united within a thin protective band resisting to temperatures up to 240° C. At the center of said thermoplastic sleeve, a circuit element for voice transmission based on two parallel metal conductors is arranged. Each one of said metal conductors is opposed to the helical union of the first circuit.
Thus, for example in U.S. Pat. No. 4,761,053, an overhead lead-in cable is described which includes a rectangular cross-section sleeve with two tension members based on various filaments impregnated with a sleeve compatible material. Each said member is arranged opposite a pair of conductors and at least one of them is made of optic fiber and vertically aligned, in parallel.
In U.S. Pat. No. 5,180,890, a cable is described which is also of a rectangular type, including two tension members, one placed at each end of the sleeve and two copper conductors separated and horizontally aligned, in parallel.
In U.S. Pat. No. 5,155,304, an overhead lead-in cable is described with an embodiment of 4 or more tension members based on intertwined filaments impregnated with a plastic material forming a reinforcement thread for the catenary elongation tension. Said overhead lead-in cable also has two or more insulated copper conductors placed in the center of the thermoplastic sleeve, vertically aligned and in parallel or in the shape of a cross forming and interstice between the insulated conductors.
The applicant has developed an improved VVDL-type lead-in cable for overhead or underground installation, based on a design of self-supporting elements for overhead lead-in lines and a dedicated circuit permitting a high-speed digital signal transmission without interfering at all with the voice service signals or the use of additional electronic circuits to separate the signals. The design that is also highly resistant to diaphony, is characterized because it has a core of two insulated conductors impregnated with a surrounding layer of moisture absorbing swelling powder.